An exhaust collector or else exhaust manifold combines the exhaust gases from a plurality of cylinders of an internal combustion engine. In the case of an air gap-insulated exhaust collector, at least one inner shell body, which is provided to conduct exhaust gases, is sheathed by an outer shell body so as to form a thermally insulating air gap. The use of air gap-insulated exhaust collectors allows the thermal loading of an engine unit or a cylinder head, onto which the exhaust collector is flanged, to be reduced.
In order to increase the power of an internal combustion engine, it is generally known to charge the fresh gas supplied to the combustion chambers with the aid of an exhaust turbocharger. For this purpose, the respective exhaust turbocharger can be connected on the exhaust gas side directly to the exhaust collector. The exhaust gas has at this point its highest temperature and its highest pressure, as a result of which very high enthalpy is available for the exhaust turbocharger. Modern turbochargers can operate in accordance with the twin-scroll principle. On the one hand, a twin-scroll exhaust turbocharger of this type has two separate inlet paths which lead from the common exhaust gas-side inlet to the common turbine of the turbocharger. On the other hand, the cylinders, which supply the turbocharger with exhaust gas, of the internal combustion engine are divided into two groups in order to separately supply their exhaust gases to one of the inlet paths of the twin-scroll turbocharger. This allows exhaust gas to be applied more uniformly to the turbine even at lower speeds of the internal combustion engine; this improves the response characteristics of the turbocharger, in particular shifts said characteristics toward lower speeds. The separate conducting of exhaust gas from the individual cylinder groups can take place via separate exhaust collectors. In the case of an air gap-insulated exhaust collector, this can also be achieved as a result of the fact that two separate inner shell bodies, which are each associated with one cylinder group, are arranged in the common outer shell body.
In particular in the case of air gap-insulated exhaust collectors, it is conventional to assemble the respective inner shell body from a plurality of individual gas-conducting components. For this purpose, the individual gas-conducting components are inserted into one another in the region of at least one slide fit. The design with slide fits reduces thermally induced stresses within the exhaust collector.
Manufacturing tolerances must be taken into account in the manufacture of the individual components of the inner shell bodies. This inevitably leads to engagement of the respective components within the respective slide fit with greater or lesser radial play. However, during operation of the exhaust collector, radial play of this type leads to leakage. As the outer shell body surrounds the respective inner shell body in a gas-tight manner, such leakages are usually uncritical. However, for the use of the exhaust collector in conjunction with a twin-scroll exhaust turbocharger, there is the need to reduce the leakages in the region of the slide fit, in particular when two inner shell bodies are arranged in a common outer shell body.